Basilisk can only be fused after getting the Rock Dragon Wing Key Item from completing the request, Time to Test Your Skills. The request involves fighting Elizabeth wielding Basilisk as her Persona, and is available after entering Evil Spirit Club 4th Story.

"A dark dragon from Northern Africa, whose name means "king of snakes".Since tales about it have been told for ages, there are various versions of it, but they are marked by their wings and crested crown. Its breath and gaze are so toxic that they will instantly kill any mortal being."